As part of this move properties/methods to the correct subclass
(position related properties go under SVGTextPositioningElement).
SVG text element hierarchy:
SVGTextContentElement
^- SVGTextPositioningElement
^- SVGTextElement
^- SVGTSpanElement
^- SVGTextPathElement (TODO)
^- SVGTRefElement (TODO)
The implementation of painting for SVG text follows the same pattern
as the implementation of painting for SVG geometries. However, instead
of reusing the existing PaintableWithLines to draw text, a new class
called SVGTextPaintable is introduced. because everything that is
painted inside an SVG is expected to inherit from SVGGraphicsPaintable.
Therefore reusing the text painting from regular text nodes would
require significant refactoring.
